Sensitive analog circuits, such as low-noise miniature microphone preamplifiers, are generally difficult to test during wafer manufacturing due to electromagnetic and acoustical noisy and hostile fabrication environments. It is therefore advantageous to measure performance parameters of a signal processing circuitry during a final test of the assembled microphone assembly. Also, due to variability during production of miniature microphones assemblies for portable terminals and hearing instruments, it is advantageous to measure performance parameters on the assembled microphone assembly to ensure compliance with electrical and/or electro-acoustical specifications. Electro-acoustic sensitivity (Volt/Pascal) and electrical output noise level of a low-noise miniature microphone preamplifier are examples of such performance parameters.
However, measurements of the performance parameters are typically influenced by an interaction and combination of signals generated by a microphone transducer element of the assembly, and signals generated by a signal processing circuitry involving circuitries such as preamplifiers, voltage regulators, voltage multipliers etc. In order to measure performance, parameters of the assembly the signals processed or generated by the signal processing circuitry need to be separated from signals generated by the microphone transducer element.
Thus, it may be seen as an object of the present invention to provide an integrated diagnostic or test circuitry for separating the signals generated by the signal processing circuitry from signals generated by the microphone transducer element. By doing this, accurate identification of a failing component or part of a rejected miniature microphone assemblies is possible and the failing component can be redesigned or modified as appropriate.